Were you at the range and was the Glock loaded? There are any number of conditions where it could feel like there was something "loose" inside the weapon. The 1911's we had in the USMC would rattle when you shook them 35 years ago, but they shot every time and generally hit what we aimed at. If the weapon was unloaded and not fully in battery, the barrel itself could have been moving, sometimes you can hold the UNLOADED weapon in one hand and move the slide/barrel assembly slightly, enough to feel motion. Again, what was the condition of the weapon? Let us know and we can diagnose further.

the gun was empty, not ready to shoot. yeah you could clearly feel rattle inside. did not feel like a barrel thou. like something small inside. thanks for help.

Glock has an internal lock system that is activated by certain movements I noticed the same thing on the Glock 17

Its the striker (firing pin). Its supposed to do that.

BJ, Is it that the striker fired weapons like the Glock and the S&W M&P place the striker in tension and only the trigger movement will then fully cock and release the striker which has the striker in tension, therefore, doesn't rattle at that time. Is the above an accurate assesment? I own a S&W M&P 40 and a Glock 22 from the S.O., I don't shoot them much as I usually shoot the Beretta 96's and my 92FS, Sig 2340, Cougar 8000 in .40, or my H&K USP 40. I'm pretty into hammer fired weapons and am not really comfortable with the Glock grip or grip angle. I do like to understand operation and nomenclature on all my weapons though. Just let me know if I am correct in my assement above.